find the x-intercepts of:
x^4-2x^3-8x^2+12x-16
In other words, you want the solutions of
x^4 -2x^3 -8x^2 +12x -16 = 0
If there are any integral roots, they are even divisors of 16. Try +or- 1,2,4,8 and 16.
None of those roots work, so you must resort to numerical methods.
Try using
http://www.hvks.com/Numerical/websolver.php